IntroductionQuantum computing has become a major buzzword of the current decade, and there is broad consensus that it will be one of the most critical future technologies. However, many scientists considered it unachievable until in recent years preliminary demonstrations proved otherwise. In the last decade quantum computing has finally escaped the realm of pure academic interest, with major industry players entering the quantum computing race and major developments rapidly taking place. The race for quantum supremacy has already been won in the context of NISQ (noisy intermediate scale quantum) devices, with the next major milestone being scalable, universal quantum computing, one that is likely to be achieved in the coming decade. This milestone will have far-reaching implications in technology, business, materials research, medicine, and everyday life via cloud-based applications.The internet has arguably been the most transformative technology of the last two decades. With the advent of quantum technology,
Error-detection and correction are necessary prerequisites for any scalable quantum computing architecture. Given the inevitability of unwanted physical noise in quantum systems and the propensity for errors to spread as computations proceed, computational outcomes can become substantially corrupted. This observation applies regardless of the choice of physical implementation. In the context of photonic quantum information processing, there has recently been much interest in passive linear optics quantum computing, which includes boson-sampling, as this model eliminates the highly-challenging requirements for feed-forward via fast, active control. That is, these systems are passive by definition. In usual scenarios, error detection and correction techniques are inherently active, making them incompatible with this model, arousing suspicion that physical error processes may be an insurmountable obstacle. Here we explore a photonic error-detection technique, based on W-state encoding of photonic qubits, which is entirely passive, based on post-selection, and compatible with these near-term photonic architectures of interest. We show that this W-state redundant encoding techniques enables the suppression of dephasing noise on photonic qubits via simple fan-out style operations, implemented by optical Fourier transform networks, which can be readily realised today. The protocol effectively maps dephasing noise into heralding failures, with zero failure probability in the ideal no-noise limit.
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